#tidytuesday for US tuition data

tuition.R

library(tidyverse)

# download from https://github.com/rfordatascience/tidytuesday/blob/master/data/us_avg_tuition.xlsx

dat <- read_xlsx("us_avg_tuition.xlsx") %>%
  gather(Year, Tuition, -State) %>%
  separate(col = Year, into =  c("Start", "End"), sep = "-") %>%
  mutate_at(.vars = c("Start", "End"), .funs = parse_number) %>%
  mutate(End = End + 2000)

states <- data.frame(State = state.name, state=state.abb)

dat %<>% inner_join(states)

rates <- dat %>% group_by(State) %>% 
  nest %>%
  mutate(model = map(data,
                     ~glm(data = .,
                          round(Tuition) ~ Start , 
                          family = poisson()
                     ))) %>%
  unnest(model %>% map(broom::tidy)) %>%
  filter(term == "Start") %>%
  mutate(Rate = exp(estimate) - 1) %>%
  select(State, Rate) %>%
  inner_join(states)

# devtools::install_github("hafen/geofacet")
library(geofacet)

to_plot <- dat %>%
  inner_join(rates) %>% 
  mutate(Rate = 100*Rate) %>%
  mutate(rate_cut = cut(Rate, 
                        breaks = seq(floor(min(Rate)),
                                     ceiling(max(Rate))+1,
                                     by = 2))) %>%
  mutate(Start_ymd = parse_date(paste(Start, "01", "01", sep="-")))

us_state_grid2a <- filter(us_state_grid2, code != "DC") %>%
  mutate(row = ifelse(code == "MD", row - 1, row))

pdf(file = "states_trends.pdf", width = 10, height = 7)
ggplot(to_plot, aes(Start_ymd, Tuition/1000)) +
  geom_line(data=select(to_plot, -state), aes(group=State), alpha=0.025) +
  geom_line(aes(color=rate_cut), size=1) +
  facet_geo(~ state, grid = us_state_grid2a) +
  ylim(c(0,NA)) +
  xlab("Academic Year Start") +
  scale_x_date(date_labels = "'%y") +
  scale_color_manual(values=RColorBrewer::brewer.pal(length(levels(to_plot$rate_cut))+1,"Reds")[-1],
                     name="Annual average percent increase in tuition") +
  ylab("Annual Tuition (1000 USD)") +
  theme_bw() +
  theme(legend.position = "bottom", panel.grid.minor = element_blank()) +
  labs(title="Rising tuition costs at four year public colleges",
       subtitle="Data from College Trends (2015)")
dev.off()